Kent L. Knoernschild

Electrochemical behavior of titanium in artificial saliva: Influence of pH

Titanium is the most common material chosen for dental implants because it is highly corrosion resistant because it constantly reforms a protective passive film layer. The formation and composition of the passive film layer is dependent on the environmental conditions. If the stable oxide layer is damaged, the titanium surface underneath can corrode. The purpose of this study was to determine if basic corrosion of commercially pure titanium (CpTi) alloy in artificial saliva was affected by pH and to understand the corrosion kinetics/mechanisms of CpTi as a function of pH. In this study, titanium alloy discs were subjected to corrosion tests. Before the tests, all samples were cleaned and polished using standard metallographic preparation methods. Artificial saliva was used as the testing medium. The following pH values were tested: 3.0, 4.5, 6.0, 6.5, 7.5, and 9.0. Different pH values were achieved by adding lactic acid (acidic) or NaOH (basic) in appropriate amounts. Potentiodynamic curves indicated behavior change at each pH. In addition, the corrosion current density value determined from the potentiodynamic curve exhibited the poorest corrosion resistance for pH 7.5. The Nyquist plot (from the electrochemical impedance spectroscopy results) indicated that pH 7.5 had the poorest resistance. Scanning electron microscopy images indicated that pH levels of 6.5, 7.5, and 9.0 had considerable surface corrosion. The results showed that the medias pH significantly influenced the corrosion behavior of CpTi. The poor corrosion behavior at the neutral pHs invites some concerns and highlights the need for further study.

Effect of repeated screw joint closing and opening cycles on implant prosthetic screw reverse torque and implant and screw thread morphology

STATEMENT OF PROBLEM Clinicians must know if a new screw can predictably increase reverse torque after multiple screw insertion cycles. PURPOSE The purpose of this study was (1) to compare the effect of multiple implant prosthetic screw insertion and removal cycles on reverse torque, (2) to determine whether a new screw, after multiple screw insertion cycles, affects reverse torque, and (3) to assess implant and prosthetic screw thread surface morphology with scanning electron microscopy (SEM). MATERIAL AND METHODS One primary screw was paired with an implant (MT Osseospeed) and inserted to 25 Ncm torque 9, 19, 29, or 39 times (n=10). Primary screw reverse torque values were recorded after each insertion. A second, reference screw was then paired with each implant for a final screw insertion, and reverse torque was measured. Maximum, minimum, median, and mean values (P(max), P(min), P(median), and P(mean)) were identified for primary screws. A 1-way ANOVA and Tukey HSD post hoc analysis assessed the influence of multiple screw insertion cycles on P(max), P(min), P(median), and P(mean) values (α=.05). Confidence intervals were used to test differences between reference (REF) screw data and corresponding DMAX and DMIN (DMAX=P(max)-REF; DMIN=P(min)-REF). The surface topography of an unused implant and screw and of 1 implant and screw from each group was evaluated with SEM. RESULTS Pairwise comparisons showed that 9 or fewer insertion cycles resulted in significantly greater mean reverse torque (20.9 ± 0.5 Ncm; P<.01). After 19, 29, or 39 cycles, the second, reference screw achieved significantly greater reverse torque than the minimum recorded values (P<.05). Implant thread surface morphology changes occurred primarily during the first 10 insertions. CONCLUSIONS After 10 screw insertion cycles, a new prosthetic screw should be used with the implant system tested to maximize screw reverse torque and maintain preload when an abutment is definitively placed.

Influence of corrosion on lipopolysaccharide affinity for two different titanium materials.

STATEMENT OF PROBLEM Titanium is subject to corrosion in the oral cavity, which could contribute to periimplantitis. However, the effect of corrosion on the lipopolysaccharide affinity for titanium remains unknown. PURPOSE This study evaluated the role of corrosion (in artificial saliva at pHs 3, 6.5, and 9) on the lipopolysaccharide (LPS) affinity for commercially pure titanium (cp-Ti) and Ti-6Al-4V alloy. MATERIAL AND METHODS Seventy-two titanium disks were anodically polarized in a controlled environment (n=9). Control specimens were not corroded. Deionized water with different concentrations of LPS (1.5, 15, and 150 μg/mL) were used to treat the disks for 24 hours to investigate LPS adherence (n=3). Then specimens were immersed in LPS-free water to evaluate LPS elution at 24, 48, and 72 hours. Data were analyzed by the 2-way, 3-way, and 3-way repeated measures ANOVA, t tests, and the Tukey honestly significant difference (HSD) tests (α=.05). RESULTS A greater corrosion rate of cp-Ti and Ti-6Al-4V alloy and a higher LPS adherence to titanium surfaces (P<.05) were noted at acidic pH. The LPS affinity was higher for the Ti-6Al-4V alloy than for cp-Ti (P<.05). More LPS was eluted from titanium surfaces after a 24-hour interval. CONCLUSION Lipopolysaccharide affinity for cp-Ti and Ti-6Al-4V alloy is influenced by the corrosion process.

Early survival of single-tooth implants in the esthetic zone may be predictable despite timing of implant placement or loading.

SELECTION CRITERIA The authors used MEDLINE, EMBASE, and CENTRAL (Cochrane Central Register of Controlled Trials) databases to locate studies for this systematic review (SR). For studies to be eligible for this SR, all had to evaluate single-implant restorations with a follow-up of at least 1 year after implant loading. A total of 19 prospective studies met inclusion and exclusion criteria. Fifteen studies provided implant survival data (499 patient/509 implants), whereas 5 studies provided radiographic marginal bone height data (52 patients/52 implants). The analysis included studies with patients with single anterior or premolar,maxillary or mandibular edentulous sites bounded by anterior and posterior neighboring teeth. Meta-analyses of prospective trials (randomized-controlled trials, clinical trials, cohort studies, case series) reported loaded implant survival with one-year or more than one-year follow-up. Meta-analysis of prospective trials reporting marginal bone loss with one-year follow-up was also reported. KEY STUDY FACTOR The key interventions were the timing of implant placement following extraction and the timing of implant loading after implant placement. Comparisons following greater than one-year follow-up were made between implants with immediate placement with immediate loading, immediate/early placement with conventional loading, conventional placement with immediate/early loading, or conventional placement with conventional loading. MAIN OUTCOME MEASURE The main outcome was implant survival. Radiographically determined peri-implant bone level change was also reported. Meta-analyses were completed using studies that reported one-year implant survival data (15 studies) and more than one-year implant survival data (11 studies). One-year marginal bone level data were analyzed for implants treated conventionally (5 studies). For survival and marginal bone levels, weighted rates and random effects models were used to calculate overall effects of the included studies. For greater than one-year follow-up, survival data were stratified by intervention type. Results were weighted for study size and stratified based upon timing of implant placement and loading. Esthetics, and patient satisfaction, and complications were reported, but heterogeneity of study design and reported outcomes excluded the results from meta-analysis. MAIN RESULT Approximately two-thirds of patients received implants in healed edentulous sites. Survival of single-tooth implants one year in function was 95.5% [95% CI: 93.0-97.1]. Meta-analysis identified no difference in survival rate at one year when the results were weighted for study size and stratified based upon timing of implant placement and loading. Survival of single-tooth implants more than one year in function ranged from 92.4% [95% CI: 84.4-96.4] for conventional placement with immediate loading to 97.5% [95% CI: 88.3-99.5] for immediate placement with immediate loading. The third meta-analysis identified 0.20-mm [95% CI:0.034-0.36] marginal bone loss for implants one year in function. Qualitative interpretation of other esthetic, patient satisfaction, and complication outcomes revealed no difference in immediate, early, or conventional therapy approaches. CONCLUSIONS The authors concluded that implant-supported single-tooth replacement in the aesthetic zone with adjacent natural teeth can lead to short-term, favorable outcomes with regard to implant survival and marginal bone level change with early/immediate or conventional surgical placement and loading strategies.

An Analysis of Prosthodontic Research Productivity: Geographic, Economic, and Collaborative Perspective

PURPOSE This study evaluated the quantity of prosthodontic literature produced globally by continent in three prosthodontic journals over a 10-year period, 1998-2008. Prosthodontic research productivity relative to economic status of countries and collaboration among countries grouped by economic status was assessed. MATERIALS AND METHODS Three peer-reviewed prosthodontic journals were used for the analysis of articles published in 1998, 2003, and 2008: The Journal of Prosthetic Dentistry, International Journal of Prosthodontics, and Journal of Prosthodontics. The country of every author listed for each included article was recorded. The number of articles published by each continent and each country was reported. Countries were grouped according to the World Bank economic classification system, and the number of articles published by each economic class was found. RESULTS The majority of publications over the 10-year period were produced in Asia (Japan), Europe (Germany), and North America (USA). Productivity declined by 14.4% in high-income countries while it increased in upper middle-, lower middle-, and low-income countries. The majority of publications written by upper and lower middle- and low-income countries were independent works. Articles resulting from collaboration increased over time for all economic classes of countries. CONCLUSIONS The origins of prosthodontic literature are becoming more geographically and economically diverse, with increased contributions from Africa, Asia, and South America, and middle- and low-income countries between 1998 and 2008. Collaboration between high-income countries and the other economic group countries increased over time.

Resident selection criteria for advanced education in prosthodontic programs: program directors' perspective.

PURPOSE The purpose of this study was to describe the criteria used by advanced education in prosthodontic program (AEPP) directors to select their residents, to rank them by perceived importance, and further assist prospective candidates with the application process for AEPP. MATERIALS AND METHODS Questionnaires were distributed to all prosthodontic program directors (N = 46). The program directors were requested to respond in five sections: (1) general information, (2) information obtained from applications and letters of recommendation, (3) interview process, (4) decision process, and (5) retrospective view of the selection process. Descriptive statistics were used to analyze the data. Data were collected and compiled into mean, standard deviation, and range. Results were tabulated and ranked. RESULTS Thirty-eight responses (82.61%) were returned and analyzed. Most of the programs (75.77%) indicated that a combination of the program director, current residents, prosthodontic faculty, and staff members were involved in conducting the interview process. Factors considered very important when choosing applicants to the prosthodontic program were (1) interview process, (2) dental school class rank, (3) dental school grades (prosthodontics), (4) letters of recommendation, (5) dental school grades (clinical). Letters from the prosthodontic post-doc program director and prosthodontic faculty were considered the most important source of recommendation. Honesty, organization, and energy were ranked as the most positive characteristics of the applicants during the interview. Almost all respondents (97%) were satisfied with the current selection process. When asked about the current applicant pool, most program directors (91.67%) were satisfied. CONCLUSIONS The most and least important factors in selecting applicants by the program directors were described and ranked. This study was intended to provide the profession with some insight on how advanced Prosthodontic programs select their applicants. It may also serve as a valuable instrument for prospective applicants to AEPPs in the future.

Porphyromonas gingivalis lipopolysaccharide affinity for two casting alloys

With the exception of plaque, the affinity of biologically active bacterial products for restorative materials and the influence of that affinity on periodontal health has not been detailed. This study recognized that Porphyromonas gingivalis endotoxin, which is cell envelope lipopolysaccharide (LPS) produced by a bacterium that is common to the crevicular microbial flora, has an affinity for dental casting alloys. Regardless of surface finish, no difference in LPS initial adherence or elution was recorded between a type III gold or nickel-chromium-beryllium alloy (p > 0.05), but LPS readily adhered and remained attached to both alloys. LPS affinity could contribute to periodontal inflammation in tissues that approximate restorations fabricated from either alloy.

Retrospective analysis of dental implants placed and restored by advanced prosthodontic residents.

PURPOSE The purposes of this retrospective clinical review were to: (1) describe the demographics of implant patients, types of implant treatment and implant-supported prostheses in an Advanced Education in Prosthodontic Program, (2) evaluate the survival rate of dental implants placed by prosthodontic residents from 2006 to 2008, and (3) analyze the relationship between resident year of training and implant survival rate. MATERIAL AND METHODS All patients who received dental implants placed by prosthodontic residents from January 2006 to October of 2008 in the Advanced Prosthodontic Program at the University of Illinois at Chicago College of Dentistry were selected for this study. Age, gender, implant diameter, length, implant locations, surgical and restorative detail, and year of prosthodontic residency training were collected and analyzed. Life-table and Kaplan-Meier survival analyses were performed based on implants overall, locations, year of training, and use of a computer-generated surgical guide. A Logrank statistic was performed between implant survival and year of prosthodontic residency training, location, and use of computer-generated surgical guide (α= 0.05). RESULTS Three hundred and six implants were placed, and of these, seven failed. Life-table and Kaplan-Meier analyses computed a cumulative survival rate (CSR) of 97% for overall implants and implants placed with a computer-generated surgical guide. No statistical difference was found in implant survival rates as a function of year of training (P= 0.85). CONCLUSION Dental implants placed by prosthodontic residents had a CSR comparable to previously published studies by other specialties. The year of prosthodontic residency training and implant failure rate did not have any significant relationship.

Patient Recall in Advanced Education in Prosthodontics Programs in the United States

PURPOSE This study surveyed program directors of Advanced Education Programs in Prosthodontics (AEPP) in the United States to determine the extent, type, incidence, and perceived effectiveness of implemented recall systems. MATERIAL AND METHODS Surveys were sent to AEPP directors across the United States to assess their programs recall protocol. This survey first identified whether an active recall program existed. For programs with recall systems, rigor in promoting ongoing oral health was surveyed by focusing on recall frequency, patient tracking protocol, involved personnel, interaction with other university departments, provided clinical procedures, and therapy completion protocol. Whether the directors perceived that their recall system was successful was also investigated. RESULTS Thirty-three of 46 programs responded, giving a response rate of 72%. Of these 33 programs, only 21 (64%) had an active recall system, although 30 (91%) believed recall to be important. Twelve (57%) directors with recall programs considered their system to be effective. CONCLUSIONS Prosthodontic program directors felt their programs recall effectiveness could be improved. Due to the numerous potential benefits of an active recall system, AEPPs should consider implementing or enhancing their recall programs. Further studies are indicated to determine specific criteria that describe an effective recall system for prosthodontic programs within the context of patient health promotion, program curriculum, and financial ramifications.

Retrospective Analysis of Implant Overdenture Treatment in the Advanced Prosthodontic Clinic at the University of Illinois at Chicago.

The aim of the present retrospective study was to evaluate the clinical outcomes of implant-supported overdenture treatment provided by prosthodontic specialty residents. Twenty-three patients with 25 implant-supported overdentures (IODs) participated in the study. Seventy-four implants were placed by periodontic, prosthodontics, or oral and maxillofacial surgery students. All prostheses were fabricated in the advanced prosthodontics clinic at University of Illinois at Chicago. The condition of the peri-implant soft tissue, implants, and prostheses were evaluated. Complications and any maintenance were documented. Patients completed an oral health impact profile-14 and semantic differential scale questionnaires. Statistical analyses were performed using SPSS statistical software. Twenty mandibular and 5 maxillary IODs were evaluated. Ninety-seven percent of the attachments were locators (Zest Anchors) and 3% ball attachments. None of the implants had lost osseointegration, but 14 implants (19%) had developed marginal bone loss in one-third of the implant length or more. Fourteen (19%) implants had developed dehiscence, which ranged from 1 to 4 mm. A variation in the width of the keratinized tissue, gingival, plaque, and calculus index was observed. There was a statistically significant relationship between the presence of plaque and the bleeding on probing on the buccal aspect of implants (P = .012). The incidence of dehiscence was significantly higher on the midfacial when the keratinized tissue was less than 2 mm (P < .0001). The majority of the complications were prosthetic in nature, such as broken denture teeth (74%) and worn or loose matrices (35%). Debris was observed in 19% of the locator abutments, and 36% of the overdentures were not stable in application of anterior force. Patients were compliant with oral hygiene protocols and their chewing ability was high (mean = 8.0). The overall experience was pleasant (mean = 7.5); the treatment provided good esthetics (mean = 8.3) and great satisfaction (mean = 8.5). From an educational and clinical perspective, IOD therapy has been documented to be a predictable and successful treatment option. Patients should be informed of the required maintenance and the possible complications related to IOD therapy.